Improvements over time in alloying techniques have led to the development of so-called superalloys. The term superalloy is generally used in reference to high performance alloys exhibiting increased mechanical strength and creep resistance at high temperatures. Superalloys also generally exhibit good surface stability, as well as corrosion and oxidation resistance.
Superalloys are generally composed of a base alloying element, such as nickel, cobalt, or nickel-iron, and include a variety of further alloying elements. The development of superalloys has arisen from not only chemical and process innovations, but also from the need for high performance articles formed from such alloys, and such development has been driven particularly by industries (such as the automobile, aerospace, and power industries) that use parts requiring high performance ability. In particular, superalloys have found great use in forming turbine wheels, such as for jet engines.
During operation of jet and land-based turbine engines, high temperatures and stresses are normally encountered. In order to function properly over extended periods of time, the components within these turbine engines must retain high strength and other properties at temperatures in excess of 454° C. (850° F.). Nickel-based superalloys have long been recognized as being useful for preparing parts, such as turbine wheels, having properties at elevated temperatures that are superior to those of steel-based components, and which meet the performance requirements of turbines.
Many nickel-based superalloys are known in the art. One particular example is the alloy MAR 247, which is particularly used in turbine wheels for achieving higher vibration strength. It is a nickel-based alloying including a relatively large amount of cobalt, as well as other high cost elements, such as tantalum and hafnium. The increased cost associated with the preparation of such alloys, however, is highly unfavorable.
Examples of further nickel-based alloys known in the art are disclosed in U.S. Pat. Nos. 6,482,355; 6,410,153; 6,207,291; 5,895,516; 5,298,052; 4,995,922; 4,692,305; 4,019,900; 3,810,754; 3,494,709; 3,166,413; 3,475,165; 2,968,550; and 2,868,639. Despite these various disclosures, there yet remains a need for alloys useful for preparing articles capable of performing at high temperature. Moreover, it is desirable to prepare such alloys while reducing the high cost commonly associated with the components necessary to prepare such alloys.
The need for articles prepared from superalloys continues to increase with time. It is anticipated that exhaust gas temperatures in passenger car engines will continue to increase as the output of such engines continues to increase. Moreover, it is anticipated that applications for gasoline-fueled engines will continue to increase. Accordingly, it is necessary to prepare engine parts, such as turbine wheels, capable of operating at increased temperatures, up to as high as 1050° C. (1922° F.).
One lower-cost alternative as a material for turbine wheels in ordinary passenger cars is INCONEL® 713C. While this material offers reduced cost, it is unable to provide the mechanical properties of higher strength alloys, such as MAR 247. Heretofore, there has not been provided a lower cost alloy composition that still provides the mechanical properties needed in applications, such as described above. The present invention, however, provides such a superalloy.